This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-235820, filed Aug. 3, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a lighting panel and a display device in which the lighting panel is used and, particularly, to a lighting panel having a light-collecting function of collecting and emitting incident light rays introduced from a light source or the outside.
2. Description of the Related Art
In a liquid crystal display device, for example, a liquid crystal display panel does not have a self-emission capacity and, therefore, a lighting panel is disposed as a back light on the rear surface side of the liquid crystal display panel. FIG. 24 is a side view of part of an example of such a conventional liquid crystal display device. The liquid crystal display device comprises a liquid display panel 1 and a lighting panel 11 which is disposed on the rear side opposite to the front surface side of the panel which is the observation side.
The liquid crystal panel 1 is configured in such a manner that a glass substrate 2 on the front surface side and a glass substrate 3 on the rear surface side are bonded together through a sealing member (not shown) in the form of a substantially square frame, and that a liquid crystal (not shown) is sealed in a space enclosed by the two glass substrates 2, 3 and the sealing member. A polarizer 4 on the front surface side is bonded to the front surface of the glass substrate 2 on the front surface side and a polarizer 5 on the rear surface side is bonded to the rear surface of the glass substrate 3 on the rear surface side.
The lighting panel 11 includes a light guide plate 12 provided on the rear surface side of the liquid crystal panel 1. The light guide plate 12 has a flat square shape. The surface of the light guide plate 12 opposed to the liquid crystal panel 1 serves as an emission surface 13 from which light is emitted, and a prescribed end surface (the left-hand end surface in FIG. 24) of the light guide plate 12 serves as an incidence surface onto which light is incident. The light guide plate 12 is configured in such a manner that an inclined surface 15 is formed so that the thickness of the light guide plate 12 becomes gradually small, along the rear surface on the rear side with respect to the emission surface 13, from the side of the incidence surface 14 to the side of an end surface 12a opposed to the incidence surface 14.
A reflector 16 is attached to the inclined surface 15 of the light guide plate 12. A cold cathode fluorescent tube (a light source) 17 is provided in a position facing the incidence surface 14 of the light guide plate 12. An end portion of the reflecting sheet 18 which covers the cold cathode fluorescent tube 17 is attached to the front surface on the incidence surface side 14 of the light guide plate 12, and the other end portion is bonded to the rear surface on the incidence surface side 14 of the reflector 16.
Light coming from the cold cathode fluorescent tube 17 and light reflected by the reflecting sheet 18 are caused to be incident onto the incidence surface 14 of the light guide plate 12. The incident light propagates (is guided) through the light guide plate 12 from the incidence surface 14 toward the end surface 12a, is reflected by the reflector 16, emitted from the emission surface 13 and caused to be incident onto the rear surface of the liquid crystal display panel 1, and is caused to irradiate the liquid display panel 1 from the rear surface side thereof. Then, image light corresponding to the display drive of the liquid display panel 1 is emitted from the front surface of the liquid display panel 1.
In the above conventional liquid crystal display device, it is possible to uniformize the luminance distribution of light emitted from the front surface of the liquid crystal display panel 1 by uniformizing an amount of light emitted from the emission surface 13 of the light guide plate 12. Next, this principle will be described below. On the inclined surface 15 of the light guide plate 12 are provided a large number of spot-like light control patterns in black ink in such a manner that the density of spot-like black patterns decreases gradually as they become away from the incidence surface 14, in other words, the absorptance of incident light decreases in proportion to the distance from the incidence surface 14.
More specifically, because near the cold cathode fluorescent tube 17, the intensity of the light which is reflected by the reflector 16 of the light guide plate 12 and emitted from the emission surface 13 toward the liquid crystal display panel 1 is high, the black pattern density formed on the inclined surface 15 of the light guide plate 12 is increased in order to increase the absorptance of the light reflected by the reflector 16. However, because the intensity of the light reflected by the reflector 16 decreases with increasing distance from the cold cathode fluorescent tube 17, the black pattern density formed on the inclined surface 15 of the light guide plate is gradually reduced so that the absorptance decreases gradually. As a result, the intensity of the light emitted from the emission surface 13 of the light guide plate 12 becomes uniform over the whole surface.
In the above conventional liquid crystal display device, because a large number of spot-like light control patterns in black ink are provided on the inclined surface 15 of the light guide plate 12, part of light is absorbed by the light control patterns. This poses the problem that the utilization efficiency of light is low, resulting in a decrease in luminance. BRIEF SUMMARY OF THE INVENTION
The object of the invention is to provide a lighting panel capable of improving the utilization efficiency of light and a display device in which the panel is used.
In a first aspect of the invention, an optical surface constituted by a large number of continuous optical elements is provided on a light guide plate. Each optical element has a curved surface, which refracts part of light introduced from the incidence surface toward the end surface at a low angle along a plane parallel to the emission surface, and an inclined surface which refracts part of light refracted by the curved surface toward the emission surface.
In a second aspect of the invention, on a light guide plate which has an incidence surface on which light emitted from a point light source is incident, there is formed an inclined surface which is extended in a direction substantially parallel to the incidence surface.
In a third aspect, an optical sheet is disposed on the side of an emission surface of a light guide plate. The optical sheet causes light emitted from the emission surface of the light guide plate in a direction substantially perpendicular to the emission surface to pass therethrough without any change, and converts light emitted in a slant direction from the emission surface of the light guide plate toward an end surface of the light guide plate into light to be emitted from the front surface of the optical sheet in a direction substantially perpendicular to the emission surface of the light guide plate.
According to the first aspect of the invention, owing to the optical surface formed on the light guide plate, which has the curved surfaces and inclined surfaces, also on a distal end remote from the incidence surface of the light guide plate, light introduced from the incidence surface is sufficiently refracted to the emission surface of the light guide plate. Therefore, the utilization efficiency of light can be improved.
According to the second aspect of the invention, light introduced from the point light source is refracted in a direction parallel to the incidence surface by means of the inclined surface which is extended in a direction substantially parallel to the incidence surface. Therefore, the utilization efficiency of light can be improved.
According to the third aspect of the invention, light emitted in a slant direction from the emission surface of the light guide plate toward the end surface is converted by means of the optical sheet in a direction substantially vertical to the emission surface of the light guide plate. Therefore, the utilization efficiency of light can be improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.